This invention relates to a beverate brewing apparatus, and more particularly, to improvement of the sealing conditions between a brewing liquid cylinder and a piston in such apparatus during a brewing operation.
Beverage brewing apparatus suitable for use in a vending machine for preparing single cup quantities of beverages from a beverage material is well known in the prior art. For example, U.S. Pat. No. 3,349,690 issued to William Heier discloses one construction for such a brewing apparatus.
Referring to FIG. 1 on the drawings, the basic construction and brewing cycle for a prior art apparatus will be described. Frame 1 of the apparatus supports a vertically movable open-bottom cylinder 2 which has the bottom opening covered by a filter member 3. A vertically movable piston 4 is disposed within cylinder 2 and relative movement between cylinder 2 and piston 4 is created by operation of a cam member 5 driven by motor 6. One end opening of a duct 7 is connected with a water tank (not shown) through an electromagnetic valve 9, this end opening being closely placed above the upper opening of cylinder 2 to supply hot water into cylinder 2. A brewing cavity 10, which is generally reciprocal horizontally between a brewing position (this position being shown by solid lines in FIG. 1) and a rest position (this position being shown by dot-dash lines in FIG. 1), is placed beneath the cylinder 2 and sealed with the lower portion of cylinder 2 in the brewing position.
The prior art apparatus is also provided with a coffee hopper 11 which is connected with a canister 12 for receiving a charge of coffee. The ground coffee fills canister 12 which is provided with suitable feed means to deliver a predetermined quantity of fresh ground coffe into hopper 11 at a point prior to the start of the brew extracting operation.
In this apparatus, brewing cavity 10, at the start of the brewing cycle initiated by a coin operated switch for example, moves horizontally toward the brewing position from the rest position to a place beneath the bottom opening of cylinder 2. During this horizontal movement, the ground coffe is supplied into the brewing cavity 10 through coffee hopper 11 at a supply position (this position being indicated by dotted line in FIG. 1). When brewing cavity 10 is properly aligned beneath the cylinder 2, due to the operation of cam member 5, cylinder 2 moves downwardly into tight engagement with cavity 10. This forms a chamber which is filled with hot water supplied through duct 7.
Thereafter, piston 4 moves downwardly to force the water through the filter member 3 into the ground coffee in cavity 10 and through an outlet duct 13 to a cup 14 placed at a dispensing station. Before introducing coffee into the cup, the extracted coffee would be mixed with a suitable amount of sugar and/or cream, both of which are supplied from canisters 15 and 16, respectively. Thereafter, the brewing cavity 10 containing the spent coffee grounds is moved to its rest position and the grounds in brewing cavity 10 are discarded at a position which is disposed just before the rest position is reached. When brewing cavity 10 is returned to its rest position, one brewing cycle has been completed.
During the brewing cycle, particularly during the extracting operation, the sealing between the inner surface of cylinder 2 and outer peripheral surface of piston 4 should be very good to effect the most favorable extracting operation. Therefore, as clearly shown in FIGS. 2 and 3, piston 4 is provided with a sealing member 17 at its outer peripheral surface. This sealing member 17 comprises, as shown in FIGS. 2 and 3, a ring portion 171 fitted on the outer peripheral surface of piston 4 and a seal portion 172 extending outwardly from ring portion 171. On the other hand, cylinder 2 is normally formed by an extrusion process. Therefore, the outer diameter of the bottom portion of cylinder 2 is slightly smaller than the outer diameter of the upper portion of cylinder 2, i.e., the wall surface of cylinder has a slant angle .theta..sub.1 related to a vertical plane, as shown in FIG. 3.
With this construction of seal element 17 and cylinder 2, as piston 3 moves downward, the friction force between the inner surface of cylinder 2 and seal element 17 increases, and finally the outer edge of seal portion 172 becomes partly turned up by the friction contact between cylinder 2 and seal element 7. The turned up portion creates a gap between the cylinder and seal element such that the extracting operation becomes inefficient or defective.